This invention relates to a fluorescent lamp device particularly of an oblate section type in which the lighting means is integrally mounted on a fluorescent lamp having an oblate cross section and, in particular, to a fluorescent lamp device which reduces the thickness of the fluorescent lamp and improves the efficiency of the lamp.
A known art has provided a flat-type fluorescent lamp device of the type in which the flat-type fluorescent lamp is electrically connected to a lighting circuit thereof and fixed to the mounting board is disclosed, for example, in Japanese Utility Model Laid-Open Publication No. 58-130352.
In the above-mentioned example, the fluorescent lamp has a luminous surface with a substantially U-shaped plan-view configuration, and an exhaust tube, which is provided at one end of the lamp, is covered with a protective cap and fitted into a substantially U-shaped holder, which is provided on the mounting board, thus securely positioning the lamp on the mounting board.
While one end of the fluorescent lamp is thus being held in position, electrode leads thereof, which extend horizontally outwards from the other end of the lamp, are respectively inserted into the fitting holes of a lampholder, which is attached to the mounting board, thereby fixing the other end of the fluorescent lamp to the mounting board and electrically connecting it to the associated lighting circuit through the lampholder.
The conventional fluorescent lamp device of the described type involves a problem such that the attaching of the lighting circuit has to be effected separately from that of the fluorescent lamp. Accordingly, when the fluorescent lamp device is incorporated into the display panel of a liquid crystal television set, for example, or the like as a backlighting, attaching members for separately attaching the fluorescent lamp and the lighting circuit have to be provided, with the number of attaching steps being inevitably large.
Furthermore, since the fluorescent lamp and the lighting circuit are not integrally attached to each other, the size of the entire device is rather large.
Generally speaking, it is required that such a fluorescent lamp be as thin as possible and, at the same time, it has to provide high and uniform liminance. Japanese Patent Laid-Open No. 62-208537 discloses a fluorescent lamp having an oblate cross section, which is an example of a fluorescent lamps which meets the above requirements.
However, as a result of the excessive reducing of the bulb thickness of a fluorescent lamp, the following problem has occurred. Namely, when the bulb flatness, which is the ratio of the length in the longitudinal direction of the flat bulb section (hereinafter referred to as the longer diameter) to the length in the lateral direction of the same (hereinafter referred to as the shorter diameter), exceeds a certain value, undesirable phenomena, such as the so-called discharge concentration and positive column swinging, are caused, thereby making it impossible to stabilize the lighting condition.
It is known, that, apart from the bulb flatness mentioned above, the discharge stability of a fluorescent lamp of this type depends upon the pressure of the filling gas, which consists of rare gases, in particular, argon, and the discharge current density, which is a value obtained by dividing the discharge current between the pair of cold cathodes of a bulb by the area of the bulb section.
However, conditions for stabilizing the above discharge and thus obtaining a highly efficient fluorescent lamp which can be used in a practical manner still remain unknown.
Accordingly, no conventional fluorescent lamps of this type have been able to simultaneously meet the two requirements of substantially reducing the bulb thickness and improving the efficiency of the lamp.